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Available online at www.ewijst.org ISSN: 0975-7112 (Print) ISSN: 0975-7120 (Online) Environ. We Int. J. Sci. Tech. 8 (1) 37-54
Environment & We An International Journal of Science & Technology
Influence of Catchment Land Cover Dynamics on the Physical, Chemical and Biological Integrity of Wetlands T.V.Ramachandra, 1, 2, 3*, D.S. Meera1 and B. Alakananda
1#
1
Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560 012, INDIA 2 Centre for Sustainable Technologies (astra), Indian Institute of Science, Bangalore – 560 012, INDIA ,3 Centre for infrastructure, Sustainable Transportation and Urban Planning [CiSTUP] Indian Institute of Science, Bangalore – 560 012, INDIA *E mail:
[email protected],
[email protected], #
[email protected], Tel : 91-80-23600985/22932506/22933099 Fax : 91-80-23601428 [CES-TVR]
Abstract Land use and land cover (LULC) changes in the wetland catchments are the direct and indirect consequence of human actions to secure essential resources. These changes encompass the greatest environmental concerns of human populations today, including loss of biodiversity, pollution of water and soil, and changes in the climate. Monitoring and mitigating the negative consequences of LULC while sustaining the production of essential resources has therefore become a major priority today. This communication investigates the effect of land-cover and water quality on distribution of diatoms in selected wetlands of Bangalore. In this respect, water quality (chemical and biological) was assessed along with LULC of respective wetland catchments. Spatial analysis has been done using remote sensing data and geographic information system (GIS). Diatoms, the major primary producers of aquatic ecosystem, respond quickly to environmental perturbations aid as bioindicators. The results showed gradients in physical, chemical and biological parameters across wetlands with different LULC. The diatom community results, when compared to chemical analyses, proved useful in providing an indication of the quality of waters. Pollution tolerant taxa such as Nitzschia palea dominated at sites with heavy inflow of sewage while, Cymbella sp. and Gomphonema sp. present abundantly at less pollution sites. Across the land-cover types, wetlands catchment comprising more of built-up area reflected higher nutrient and ionic levels, whereas wetlands with high vegetation cover showed oligotrophic water quality conditions. Species belonging to the genera Gomphonema, Cyclotella, Nitzschia and Achnanthidium expressed clear ecological preferences. This study emphasizes the need for conservation efforts at catchment level for conservation of wetlands biota. Keywords: Land use land cover (LULC), landscape, landscape dynamics, wetlands. Diatoms, Water quality
Ramachandra et al., / Environ. We Int. J. Sci. Tech. 8 (1) 37-54 Introduction Wetlands being one of the productive ecosystems play a significant role in the ecological sustainability of the region, providing the link between land and water resources (Ramachandra, 2008). The quality and hydrologic regime of the water resource is directly dependent on the integrity of its watershed. In recent years, the rapid urbanization coupled with the unplanned anthropogenic activities has altered the wetland ecosystem severely across globe (Vitousek et al., 1997; Grimmond, 2007). Changes in land use and land cover (LULC) in the wetland catchments influence the water yield in the catchment. Apart from LULC changes, the inflow of untreated domestic sewage, industrial effluents, dumping of solid wastes and rampant encroachments of catchment has threatened the sustenance of urban wetlands. This is evident from the nutrient enrichment and consequent profuse growth of macrophytes, impairing the functional abilities of the wetlands. Reduced treatment capabilities of the wetlands have led to the decline of native biodiversity affecting the livelihood of wetland dependent population. Decline in the services and goods of wetland ecosystems have influenced the social, cultural and ecological spaces as well as of water management. This necessitates regular monitoring of wetlands to mitigate the impacts through appropriate management strategies. LULC analysis is done using remote sensing data acquired through the space-borne sensors. Factors related to water quality are the most important pressure driving heterogeneity of biotic components at an intermediate spatial and temporal scale. Algae, the primary producers are linked with the changes in various physical (landscape) and chemical (nutrients) variables and indeed have been used as bioindicators of water quality. Among several groups, diatom-based pollution monitoring has proved to be rapid, efficient and cost-effective technique has been implemented worldwide to monitor rivers, streams and lakes (Taylor et al., 2007; Juttner et al., 2010; Karthick et al., 2011). Diatoms are the species-rich group of photosynthetic eukaryotes, with enormous ecological significance and great potential for environmental application. During the last two decades, diatoms have gained considerable popularity throughout the world as a tool to provide an integrated reflection of water quality (Atazadeh et al., 2007). The sensitivity and tolerance of diatoms to specific physical and chemical variables such as pH, electrical conductivity, nitrates, phosphates and biological oxygen demand (BOD) and inherent ecological patterns has been investigated across countries (Sabater et al., 2007; Taylor et al., 2007; Jüttner et al., 2009; Alakananda et al., 2011). Diatom community structure respond to the LULC changes in the catchment (Cooper, 1995), nutrient concentration (Potapova and Charles, 2002), riparian disturbance (Hill et al., 2000) and decreasing species richness, evenness and diversity from agriculture / forest areas to urban area (Bere and Tundisi, 2011). Walsh and Wepener (2009) report the dominance of Nitzschia sp. in the catchment with high intensity agriculture, while Navicula sp. was dominant at low intensity agriculture regions. However, studies on water chemistry of wetlands with the catchment LULC conditions and its impacts on diatom assemblages in urban scenario is scarce and needs to be investigated to evolve location specific catchment restoration measures and to mitigate the impact of anthropogenic activities in the fragile ecosystem’s catchment.
Ramachandra et al., / Environ. We Int. J. Sci. Tech. 8 (1) 37-54 Wetlands play a prominent role of meeting the domestic and irrigation needs of the region apart from being habitats for wide variety of flora and fauna. Bangalore, with a population of 9.5 million (as per 2011 census) has been rapidly urbanizing during the last three decades. Recent studies reveal that there has been 63.2% increase in built-up area with 78% loss of vegetation cover and 79% loss of wetlands (Ramachandra and Kumar, 2008). Wetlands have become vulnerable ecosystems evident from regular mass fish kill (Benjamin et al., 1996) reduction of migratory bird population (Kiran and Ramachandra, 1999) and ground water contamination (Shankar et al., 2008). Sustained inflow of the city’s sewage and industrial effluents apart from conversion of wetlands for other activities have threatened the existence of these fragile ecosystems necessitating the interventions to restore and sustainable management with location specific appropriate conservation strategies. Failure to restore these ecosystems will result in extinction of species or ecosystem types and cause permanent ecological damage. Wetlands function as kidneys of the landscape and help in treating the nutrients. However, the excess inflow of nutrients beyond the treatment capability results in the changes in the water quality impairing the ecological functions. Diatoms, the major primary producers of aquatic ecosystem, respond quickly to environmental perturbations, hence used as a bioindicator across continents. However, usage of diatoms as a part of environmental monitoring program in Southern Hemisphere is very limited due to inadequate knowledge on its taxonomy. Ecological optima of four dominant species were investigated for standardizing diatom indices for Indian conditions. Current study investigates the influence of LULC in the wetland catchment on diatom communities composition and distribution at spatial scale in an eco-region. LULC analysis was done using remote sensing data with Geographical Information System (GIS). Water quality was analyzed to investigate temporal variation in physicochemical parameters and their relationship with diatom community during premonsoon (August), monsoon (September and October) and post-monsoon (November) months. Study area Bangalore is located at 12o 39' N and 13o 18' N and longitude of 77o 22' E and 77o, almost equidistant from both eastern and western coast of the South Indian peninsula, and is situated at an altitude of 920 m above mean sea level. Major soil types are red loamy and laterite soil and physiography variations ranges from rocky upland, plateau and flat-topped hills forming slope at south and south east, and pedi-plains along western parts (http://cgwb.gov.in). The mean annual total rainfall is about 880 mm with about 60 rainy days a year over the last 10 years. The summer temperature ranges from 24 to 38 °C, while the winter temperature ranges from 12 to 28 °C. Bangalore is located over ridges delineating four watersheds, viz. Hebbal, Koramangala, Challaghatta and Vrishabhavathi watersheds. The undulating terrain in the region has facilitated creation of a large number of tanks providing for the traditional uses of irrigation, drinking, fishing and washing (Figure 1). Their creation is mainly attributed to the vision of Kempe Gowda and of the Wodeyar dynasty. This led to Bangalore having hundreds of such water bodies through the centuries. Recent studies reveal that there has been 63.2% increase in built-up area with 78% loss of vegetation cover and 79% loss of wetlands (Ramachandra and Kumar, 2008).
Ramachandra et al., / Environ. We Int. J. Sci. Tech. 8 (1) 37-54
Yellamma
Varthur
Vaderahalli Nelakondodd
Figure 1: Study area with India Map and Bangalore map with 4 lakes marked on the digitized vector layer of Bangalore
Four wetlands were selected for the current study. Among these Yellamallappa chetty (110 ha) and Varthur (166.87 ha) are located in Bangalore urban district and drained from densely populated area of Bangalore metropolitan (Mahadevapura zone, Population of 5,19,663). Industrial waste and agricultural runoff (Usha et al., 2008) contaminated Yellamappa chetty and Varthur together with macrophyte growth and severe sludge deposition (Ramachandra, 2008). Two other wetlands Vaderahalli (55ha) and Nelakondoddi (36 ha) are located in Bangalore Rural district with less human population and more of plantation and forested land in catchment area.
Ramachandra et al., / Environ. We Int. J. Sci. Tech. 8 (1) 37-54
Table 1: Variation in physical and chemical parameters across months at Varthur and Yellamma Wetland
Sampling site
VARTHUR INLET (Vri VTI)
VARTHUR OUTLET (VroVTO)
YALLAMMA INLET (YMI)
YALLAMMA OUTLET (YMO)
Aug
Sep
Oct
Nov
Aug
Sep
Oct
Nov
Aug
Sep
Nov
Aug
Sep
Oct
Nov
7.46
7.25
7.10
8.50
7.84
7.58
8.00
8
7.49
8.90
7.5
7.5
8.00
7.20
8
25
27.00
26.00
24.00
29.5
27.50
26.50
26
25.3
29.00
-
26.2
28.60
-
-
823
948.00
-
-
798
890.00
-
-
1083
1120.00
-
1092
863.00
-
-
654
730.00
-
-
636
700.00
-
-
865
850.0
-
870
654.00
-
-
403 92.5
550.00 110.00
82.20
-
385 83.5
563.00 81.30
62.20
-
538 42.7
620.0 44.00
70.8
537 42.8
490.00 60.50
-
38.5
0.813
0.00
1.22
0
4.065
7.15
1.63
4.06
4.227
0.00
-
5.04
1.95
0.00
-
49.95
71.54
56
95
46.28
55.28
44.7
-
33.74
117.07
35
24.29
104.07
87.9
30
293.33
197.73
133.00
314.67
192.00
298.67
-
234.66
581.33
213.33
85.33
570.66
218.67
186.70
74.67
0.05
0.27
0.157
0.299
0.03
0.28
0.162
0.24
2.57
0.85
-
0.394
0.57
0.179
-
0.21
1.94
3.217
1.637
0.05
1.73
4.175
0.718
0.51
0.61
1.94
2.98
0.44
3.3
1.813
268
256.00
240.00
336
264
236.00
292.00
420
276
320.00
360
300
284.00
296.00
288
120
120.00
144.00
88.17
132
112.00
200.00
188.17
372
132.00
68.93
280
124.00
196.00
57.71
189.92
136.00
96.00
28.261
85.392
124.00
92.00
48.757
185.232
188.00
45.838
231.68
160.00
100.00
35.107
520
55.00
440.00
140
260
56.00
-
120
420
90.00
1700
560
65.00
400.00
1580
Chlorides (mgL )
136.32
153.36
147.68
150.52
119.28
142.00
-
142
107.92
193.12
227.2
167.56
190.28
221.52
213
Sodium (ppm) Potassium (ppm)
33.6 6.8
34.30 7.00
3.1 4.4
20.05 0
34.6 6.7
31.50 6.30
0
18.93 0
40.6 7.7
40.30 7.80
22.83 0
49.5 8.5
39.70 8.20
3.9 5
23.39 0
Sampling months pH 0
Water temperature ( C) Electric conductivity (µScm-1) Total dissolved solids (ppm) Salinity (ppm) Turbidity (NTU) Dissolved Oxygen (mgL-1) Biological oxygen Demand (mgL-1) Chemical oxygen demand (mgL-1) Nitrates (mgL-1) -1
Phosphates (mgL ) Total Hardness (mgL-1) Calcium Hardness (mgL-1) Magnesium Hardness (mgL-1) Alkalinity (mgL-1) -1
** No sampling was carried out due to the Ganesha immersion.
**
Ramachandra et al., / Environ. We Int. J. Sci. Tech. 8 (1) 37-54
Table 2: Variation in physical and chemical parameters across months at Nelakondoddi and Vaderahalli Wetland NELAKONDODDI INLET (NiNKI) Aug Sep Oct Nov
NELAKONDODDI OUTLET (NoNKO) Aug Sep Oct Nov
VADERAHALLI INLET (VdiVHI) Aug Sep Oct Nov
VADERAHALLI OUTLET (VdoVHO) Aug Sep Oct Nov
8.05
8.36
8.20
8.60
7.95
7.94
8.10
8.60
9.4
9.11
8.30
8.20
8.5
9.00
8.20
8.20
Water temperature ( C) Electric conductivity (µScm-1) Total dissolved solids (ppm) Salinity (ppm)
28.4
26.30
26
26.00
26
29.50
24.5
25.00
29
27.10
24
26.00
29.5
26.10
24
25.00
711
541.00
-
-
661
582.00
-
-
550
687.00
-
-
480
608.00
-
-
564
390.00
-
-
496
441.00
-
-
300
433.00
-
-
295
468.00
-
-
351
218.00
-
-
301
256.00
-
-
255
265.00
-
-
220
278.00
-
-
Turbidity (NTU)
22.9
24.00
17.7
14.60
24.4
22.50
-
8.06
17.5
57.10
7.05
12.40
12.2
24.40
8.77
9.85
Dissolved Oxygen (mgL-1) Biological oxygen demand (mgL-1) Chemical oxygen demand (mgL-1) Nitrates (mgL-1)
10.98
6.50
8.29
10.4
7.2
7.80
6.50
11.05
5.854
9.88
1.22
-
6.667
10.73
2.76
-
5.42
6.50
5.42
18.44
14.92
16.26
3.25
13
20.34
15.00
2.03
13.7
16.00
14.00
3.9
14
32.00
20.00
13.33
17
23.00
26.67
17.60
18
32.00
26.00
8.00
16
23.00
19.50
16.00
14.4
0.08
0.18
0.085
0.254
0.06
0.11
0.084
0.153
0.06
0.14
0.634
0.149
0.08
0.06
0.161
0.327
0.017
0.16
0.046
0.052
0.004
0.02
0.225
0.11
0.025
0.13
0.008
0.046
0.1
0.04
0.098
0.028
300
232.00
160.00
160
364
240.00
204.00
180
284
148.00
148.00
172
144
148.00
160.00
500
Sampling site Sampling months pH 0
-1
Phosphates (mgL ) Total Hardness (mgL-1) Calcium Hardness (mgL-1) Magnesium Hardness (mgL-1) Alkalinity (mgL-1) Chlorides (mgL-1) Sodium (ppm)
16
88.00
80.00
24.04
36
68.00
88.00
32.06
160
36.00
60.00
32.06
76
44.00
44.00
32.06
296.096
144.00
80.00
24.388
355.216
172.00
116.00
24.384
244.96
112.00
88.00
22.432
125.456
104.00
116.00
4.86
400
87.50
240.00
666.66
420
70.00
300.00
700
340
77.50
100.00
733.33
360
67.50
260.00
566.66
31.24
187.44
130.64
113.6
39.76
184.60
136.32
122.12
31.24
139.16
127.80
136.32
34.08
130.64
110.76
127.8
60.9
44.20
3.4
19.49
71.5
44.10
3.4
18.38
32.1
35.20
2.8
18.381
31
34.70
2.6
18.93
Potassium (ppm)
3.1
2.40
1.7
0
3.7
2.60
1.6
0
3
3.20
2.5
0
2.8
3.30
2.1
0
Ramachandra et al., / Environ. We Int. J. Sci. Tech. 8 (1) 37-54
Materials and Methods Water quality analysis: Water samples from all four wetlands were collected during 4 months viz., August, September, October and November 2010. Samples collected from 10 to 30 cm below the surface of water during the morning hours and stored in disinfected plastic bottles. On-site water analysis included water temperature, pH, turbidity, salinity, electrical conductivity, total dissolved solids and dissolved Oxygen. No preservatives were added as the samples were transported to laboratory and refrigerated for subsequent analysis. Laboratory analysis includes total alkalinity, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total hardness, calcium hardness, Magnesium hardness, Potassium, Sodium, nitrates (NO3–), inorganic phosphates (PO43-) and chlorides (Cl ). These water analyses were followed as per standard procedures published by the American Public Health Association (APHA, 1998) and Chemical and Biological methods for water pollution studies, (Trivedy and Goel, 1986). Diatom analysis: Diatoms have been collected from habitats such as epilithic, (found in stones) epiphytic (found in plants) and episammic (found in sediments) of four wetlands were collected during the month of September 2010. Cleaning and identification of samples is done following Laboratory procedure as per Taylor et al., 2005 and Karthick et al., 2010. Samples are cleaned following Hot HCl and KMnO4 method and slides were prepared using Pluerax as the mounting medium. Relative abundance of each taxon was determined after counting at least 400 valves in each sample using light microscope. Identification of diatoms has been done following key characters mentioned by Krammer and Lang-Bertalot (19861991), Round et al., (1990) and Gandhi (1957a-1959d). LULC analysis: Shuttle Radar Topography Mission (SRTM) data is downloaded from CGIAR Consortium for Spatial Information (CGIAR-CSI). Digital Elevation Model (DEM) was generated using ENVI 4.7 version. The digitized Wetlands were overlayed on the DEM. The drainages were digitized using toposheet of Bangalore, 1972. Catchment of these four Wetlands was delineated using the topographic maps of 1:50000 and referring the digitized drainages. LULC for each catchment was assessed using IRS 1D data (October 2006). IRS data was geo-referenced using image-to-image registration. Training data is collected from field using pre-calibrated handheld Global Positioning System (GPS). IRS data were classified using supervised classification techniques with the Gaussian maximum likelihood classifier into three classes – vegetation, water body and built up. Accuracy assessment was done to validate the classified data. Statistical analysis: Variation in water quality and diatom species distribution across sites is analysed using PAST software, version 2.11. Canonical correspondence analysis (CCA) included data of 8 abundant diatom taxa (RA >10% at least in 1 sampling site), 17 environmental across 8 sampling sites during 4 month period to evaluate role of environmental variables (water quality and land cover type) in structuring diatom communities.
7
Ramachandra et al., / Environ. We Int. J. Sci. Tech. 8 (1) 37-54 Results and Discussion Water Quality Analysis Varthur Wetland: The overall water quality parameters measured are listed in Table 1. pH was recorded as neutral to slightly alkaline with lowest and highest at VTI (7.1) in October and VTI (8.5) in November respectively. Electric conductivity and total dissolved solids values were consistent with a narrow range of 823 to 948 mgL-1 and 636 to 730 mgL-1 respectively. Hypoxic and even anoxic condition due to low dissolved oxygen was observed at VTI site (1.22 mgL-1) and at VTO site as well with a range of 1.63 -7.15 mgL-1. This attributed to the presence of water hyacinth covering the water surface with heavy domestic organic load and decomposition of organic matter. This condition is also reflected in elevated concentrations of BOD and COD with exceeding permissible limits at all sampling sites across months (Table 1). Total hardness (236-420 mgL-1), alkalinity (55-440 mgL-1) and chlorides (119.28-153.36 mgL-1) were recorded very high due to sewage inflow. Yellamma Wetland: pH was recorded as neutral to slightly alkaline with lowest at YMO (7.20) in the month of October and highest at YMI (8.90) in the month of September. Electric conductivity and total dissolved solid values show a significant range. In September, YMO showed a less EC value of 863 µScm-1 and Yellamma inlet showed high value of 1120 µScm1 owing to high ionic concentrations inflow from industrial wastes. Dissolved oxygen content varied in both inlet and outlet ranging from 0 to 5.04 mgL-1. DO was less than measurable amount in the month of October in YMO and September in YMI reasoning to high organic load. In the month of August DO of 4.22 mgL-1 in YMI and 5.04 mgL-1 in YMO was observed. The discharge of sewage containing organic material from the nearby factories contributed to this situation. This condition was also reflected in elevated concentrations of BOD and COD with exceeding permissible limits at all sampling sites across months (Table 1). In the month of October no sampling could be done in Yellamma inlet due to blockage on account of immersion of idols (Ganesha). Nelakondoddi Wetland: pH ranged from 7.94 at NKO site (Sep) to 8.60 at both the sites (Nov) indicating slightly neutral to alkaline nature of water and within the permissible limits (Table 2). EC, TDS and salinity ranged from 480 to 687 µScm-1, 295 to 468 ppm and 220 to 278 ppm respectively indicating low mineralization in this Wetland. However, slight gradation was observed in September due to monsoon climate. DO at all sampling sites was within the permissible limit and ranged from 6.5 mgL-1 at NKI to 11.05 mgL-1 at NKO. The higher DO recorded during monsoon and post monsoon seasons (i.e., Oct and Nov) may be due to the impact of rain water resulting in aeration ( Ayoade et al., 2006). A huge variation in BOD (5.42 to 16.26 mgL-1 ) and COD (13.33 to 32 mgL-1 ) was studied across months, the highest value of BOD being in the November month (18.44 mgL-1 at NKI) and COD being highest at both sites in August month (Table 2). Vaderahalli Wetland: The pH in both sites indicates slightly alkaline ranged from 8.20 to 9.11 (Table 2). Water temperature varied depending on the time of sampling with a range of 24 to 29.5 0C. EC, TDS and salinity ranged from 541 to 711 µScm-1, 390 to 564 ppm and 218 to 351 ppm respectively indicating low mineralization in this Wetland. However, slight gradation was also observed in September due to monsoon climate. DO at all sampling sites was within the permissible limit and ranged from 5.854 mgL-1 at VHI to 10.73 mgL-1 at VHO except in October where the DO was observed to be very low. A huge variation in BOD (2.03mgL-1 to 20.34 mgL-1) and COD (8 mgL-1 to 32 mgL-1) was studied across months being 8
Ramachandra et al., / Environ. We Int. J. Sci. Tech. 8 (1) 37-54 within the permissible limits, the highest value of BOD and COD being in the August month. (Refer Table 2).
Figure 2: Variation in water quality across sampling sites [For sampling sites and its codes refer annexure I](a) pH (b) Electric conductivity (c) Biological oxygen demand (d) Chemical oxygen demand Water Quality across Wetlands The level of pollution status and spatial distribution of Wetlands from urbanized area is well reflected by water quality. Across Wetlands, pH was recorded as slightly alkaline with minimum of 7.6 at Varthur inlet and maximum of 8.75 at Vaderahalli inlet. EC, turbidity and TDS at Varthur and Yellamallappa chetty was in extremely high concentrations due to high cation concentrations. EC was more than the permissible limit at Yellamallappa chetty inlet (1101.50µScm-1) and high turbidity of 94.9mgL-1 in Varthur inlet and high TDS of 857.5 was observed in Yellamallappa chetty inlet. These parameters were low in Vaderahalli inlet with 6.18µScm-1of EC, turbidity of 13.81 NTU and total dissolved solids of 366.50 mgL-1. These parameters show marked seasonal variations (Awasthi and Tiwari, 2004). As in figure 2and 3, BOD and COD values reflected high pollution at Varthur, Yellamallappa chetty and Nelakondoddi sampling sites but contradictory values were observed in Nelakondoddi and Vaderahalli with a range of 8.959 to 12.97 mgL-1. The study by Atobatele et al., 2008 shows pH, conductivity, temperature and dissolved oxygen as important parameters contributing to the annual variability of Wetland water. Dissolved oxygen concentration was found very less in all sampling sites of Varthur Wetland and Yellamallappa chetty Wetlands compared to 9
Ramachandra et al., / Environ. We Int. J. Sci. Tech. 8 (1) 37-54 other two Wetlands, which is quite evident by heavy organic load and macrophyte cover and hence reduces redox potential of the system. Diatom Distribution Fifty eight species belonging to 29 genera has been recorded and are listed in annexure 1. The dominant taxa were Achnanthidium sp., Gomphonema. parvulum (Kutzing var. parvulum f. parvulum) Gomphonema sp., Nitzschia palea (Kutzing) W.Smith, Nitzschia umbonata (Ehrenberg) Lange-Bertalot, C. meneghiniana Kutzing, Cymbella sp. and Fragilaria sp. Most of the species occurred in polluted regions are recorded as cosmopolitan (Taylor et al., 2007). The diatom community structure shows a strong correlation with various environmental variables (Soininen et al., 2004). The species such as G. parvulum, C. meneghiniana, N. palea and N. umbonata are tolerant to high electrolyte and organic rich condition (Karthick et al., 2009) which inhabited Varthur and Yellamallappa chetty Wetlands. This clearly signifies that both these Wetlands are polluted and eutrophic in condition. Nelakondoddi and Vaderahalli show low electric conductivity, BOD and COD values and were dominated by Achnanthidium sp., Gomphonema sp. and Cymbella sp. These species were recorded as inhabiting in moderate pollution. Temporal variation and diatom distribution across Wetlands The monthly variation in water quality was reflected by diatom community composition. G. parvulum and N. palea were dominated in all months at Varthur outlet while N. linearis was recorded as abundant in October at Varthur inlet notifying the pollution level. C. meneghiniana and N. palea was dominant across months at both sampling sites in Yellamallappa chetty followed by G. parvulum in October at Yellamallappa chetty outlet. Diatom species such as Achnanthidium sp, Gomphonema sp and C. kappi (Cholnoky) Cholnoky being dominant at Vaderahallli Wetland resembled a different community structure than former Wetlands. Ecological significance of Achnanthidium sp. needs to be studied as it shows a wide range of occurrence, from oilgotrophic to slightly mesotrophic condition. Temporal variation is a significant factor responsible for changes in diatom distribution and its abundance (Sivaci et al., 2008). In Nelakondoddi outlet (NKO), N.palea, which was dominant in the month of August, was replaced by C. kappi and Mastogloia smithi Thwaites in September. However, Achnanthidium sp. dominated in October followed by Achnanthidium sp. together with Navicula sp. in November. C.kappi was dominant in September which was followed by N. amphibia Grunow f.amphibia and Achnanthidium sp. reflecting moderate trophic status. The eutrophic status and electrolyte rich was significant in November with the dominance of Fragillaria. biceps (Kutzing) Lange-Bertalot and N. linearis (Agardh) W Smith.
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a
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Species name Figure 3: Percentage relative abundance of species across months [AAugust, S-September, O-October, N-November] (a) Varthur Siddapura (b) Varthur Fishing (c) Yallamma Outlet (d) Yallamma Inlet (e) Vaderahalli Outlet (f) Vaderahalli Inlet (g) Nelakondoddi Outlet.
Relationship between dominant taxa and Water Quality CCA triplot explained 65.43% of the variability in the diatom and environmental data with 45.92% in axis 1 and 19.51% in axis 2 (Figure 4; Table 3). Monte Carlo permutation test (n=1000) showed that both axes were statistically significant (p
